The entire army of Sisera was defeated by Barak and his men who had no horses! But Sisera fled on foot to the tent of Jael, the wife of Heber the Kenite. (Jdg 4:16-17)

Evidently, Jael was not kindly disposed to Sisera. Her loyalties were with the Israelites, even though the Kenite family was on good terms with the Canaanites (Jdg 4:17).

After giving him milk to drink and covering him so he could nap, she pretended to guard his hiding place, but turned on him shortly by driving a tent peg into his temple as he slept. He died. (Jdg 4:21) So when Barak reached her tent in his pursuit of Sisera, she showed him the dead man.

These were the events recounted in Deborah's song, which Barak joined in singing.

The song begins with PRAISE: Praise ye the LORD for the avenging of Israel, when the people willingly offered themselves. Here O ye kings; give ear O ye princes; I, even I will sing unto the Lord…(Jdg 5:2, 3)

Then Deborah turned in thought to Israel's entry to the Land in the days of Moses. LORD, when thou wentest out of Seir, when thou marchedst out of the field of Edom, the earth trembled, and the heavens dropped, the clouds also dropped water.(Jdg 5:4)

The Lord began ushering his own into Canaan as they went around Mount Seir that belonged to Edom. The victory over the Amorites, just past Seir, (Num 21:21-25) trumpeted to the nations that God's people were entering — the earth trembled!

She also recalled the fiery mountain on which God's Law was delivered to Moses…The mountains melted from before the LORD, [even] that Sinai from before the LORD God of Israel.(vs 5) (Deut 5:22, 23)

This was the heritage that had been forgotten so that Israel was decimated. Deborah described the desolations: In the days of Shamgar the son of Anath, in the days of Jael, the highways were unoccupied, and the travellers walked through byways. The inhabitants of the villages ceased, they ceased in Israel, until that I Deborah arose, that I arose a mother in Israel. They chose new gods; then was war in the gates: was there a shield or spear seen among forty thousand in Israel?(Jdg 5:6-8)

Evidently, though Shamgar had fought successfully against some Philistines (Jdg 3:31), the land was not delivered from evil. John Gill's commentary describes the promised land at that time:

the public roads were so infested with thieves and robbers, who stopped all they met with, and robbed them of what they had, that travellers and merchants with their carriages were obliged either to quit their employments, and not travel at all; or, if they did, were obliged to go in private roads, and roundabout ways, to keep clear of those rapparees the highways and public roads abounded with. Not only did those Canaanitish robbers go upon the highway, and robbed all they met with, which made travelling difficult and dangerous; but entered into the villages and unwalled towns, and broke into houses and plundered them; so that the inhabitants of them were obliged to quit their dwellings, and go into the fortified cities for security; by which means the villages were left empty, and in time fell to ruin, and ceased: for they were the villages which belonged to the Israelites that were plundered, and not those that belonged to any of the Canaanites; and these were the unhappy circumstances Israel were under. (studylight.org, ibid, 1-9-13 post)

The problem was, the Hebrews had been unfaithful to the Lord (Jdg 5:8). They had thus lost the capacity to defend their lives; few had shields or spears. But from this wreckage of their society, God raised up Deborah who saw herself as a mother, loving God's children by administering his judgments.

In her song, she is inspired as a leader to praise the faithful men who stood up for the Lord and to exhort those who drew back and did not assist in defeating Sisera. Let it be known who is on the Lord's side!

Though there were prancing of their mighty ones,(Jdg 5:22) yet the Lord gave Barak the victory, and Jael was to be thanked for ending Sisera's terrible crimes. According to Judges 5:27, he fell down at Jael's feet; her blow to his head did not at first kill him, but it was enough.

Deborah's song of rejoicing ends with these beautiful words, So let all thine enemies perish, O LORD: but let them that love him be as the sun when he goeth forth in his might. And the land had rest forty years.

Like Deborah, let us strengthen the things which remain, that are ready to die, (Rev 3:2) and we shall be as that sun.